Marx produced a new theory about historical change based upon conflict between competing groups...
Einstein formulated the Theory of Relativity in 1905.
爱因斯坦于 1905 年创立了相对论。
There was a theory that he wanted to marry her...
My theory about divorce is that it's not the split-up that damages children, it's how it is handled.
He taught us music theory.
...graduates who are well-trained in both the theory and practice of statistics.
A school dental service exists in theory, but in practice, there are few dentists to work in them.